The neutron electric dipole moment (EDM) experiment has played a unique role in examining the violation of fundamental symmetries and understanding the nature of electroweak and strong interaction. A non-zero neutron EDM is one of direct evidence for CP and T violation and has the potential to reveal the origin of CP violation and to explore physics beyond the Standard Model.
A new neutron EDM experiment will be built to improve a factor of 100 by using a novel technique
of ultra-cold neutrons(UCN) in superfluid 4He at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL). In the experiment, 3He in the measurement cell will be used as a neutron spin analyzer and a comagnetometer. The absorption between UCN and 3He atoms will emit scintillation light in the superfluid 4He depending on the angle between nuclear spins of two particles. Consequently, the neutron precession frequency can be derived by the scintillation light amplitude. Furthermore, the 3He precession frequency can be measured by the superconducting quantum interference device (SQUID).
A dressed-spin technique will also be applied to measure the small precession frequency change due to
a non-zero neutron EDM. The dressed-spin technique is used to modify the effective precession frequencies of neutrons and 3He atoms to make them equal by applying an oscillatory field (dressing field) that is perpendicular to the static magnetic field. The phenomenon of the dressed spin for 3He in a cell should be demonstrated before the proposed neutron EDM experiment. A successful measurement over a broad range of the amplitude and frequency of the dressing field was done at the University of Illinois. The observed effects can be explained by using quantum optics formalism. The formalism is diagonalized to solve the solution and confirms the data.
In addition, the application of the dressed-spin technique was investigated. The modulation and the feedback loop technique should be considered with the dressed-spin technique for the measurement of the small EDM effect. The modulation of the dressing field arbitrarily changes the relative precession frequency between UCN and 3He. Through the feedback loop, the effective neutron precession frequency can be measured.
The corresponding sensitivity of neutron EDM will be estimated. A future neutron EDM experiment
could be improved if the dressed-spin technique can be carefully considered and applied.